How to tell.....

Dear tube experts,

How to tell a TFK diamond bottom smooth plate tube is a 12au7 or 12ax7 if most of the letters are missing?

Thanks!

eugeneli10-17-2006 9:15pm

boa2 Details Discussions Posts This discussion Message User 1,551 posts 10-18-2006 at 02:47am Copy Comment URL Report Comment Edit Delete You could listen to the tube. The 12AX7 will have higher gain. Are you sure these tubes are interchangeable without consequence? I thought not, but I could be wrong.
amandarae Details Discussions Posts This discussion Message User 512 posts 10-18-2006 at 04:13am Copy Comment URL Report Comment Edit Delete You need a tester.
aball Details Discussions Posts This discussion Message User 2,016 posts 10-18-2006 at 01:43pm Copy Comment URL Report Comment Edit Delete 12au7 and 12ax7 are not interchangable.
muzcal Details Discussions Posts This discussion Message User 66 posts 10-18-2006 at 04:05am Copy Comment URL Report Comment Edit Delete 1.If you can see the grid thru the holes in the plate structure, the 12au7 will have a more jagged look compared to the smoother look of a 12ax7. 2.Test it in a tube checker as if they are 12ax7's. If they meet spec, they're 12ax7's. If they are way down on the scale, they're 12au7's.